Beautiful cluster of palatal teeth of Ptychodus polygyrus,
from the Chalk. Insulated teeth of many species
of this Genus abound throughout the Chalk formation.
The mouth of these and all the other numerous extinct
species of Sharks in the family of Cestracionts, was lined
with a pavement of similar powerful teeth, forming a most
efficient apparatus, for crushing the shells of Crustacea
and Conchifera, which probably formed their principal food.
The surfaces of the Enamel are often worn away, like that
at Pl. 27 e . fig. 3. The strength and efficacy of these teeth,
viewed as Instruments for crushing shells, is very remarkable.
Beneath the Enamel, the body of each tooth is
composed of a strong mass of bone. (Miss F. C. Burgon.
Original.)

Plate 28. V. I. p. 230.

⁠Fig. 1. represents the common calmar or squid (Loligo vulgaris, Lam. Sepia loligo, Linn.) showing the place and excretory duct of its Ink bag, and the position of the feet on the anterior margin of the head. (Blainville.)

⁠Fig. 2. Side view of the Pen of the Loligo vulgaris, showing its position in the back of the animal, fig. 1. (Original.)